This paper presents a historic account of the step function which has become the basis for calculating wind loads in stability analysis. The step function used in conjunction with accepted stability criteria provides a proven level of performance but it is discontinuous and cannot be directly modelled physically. For wind tunnel testing, a continuous power law formulation is required. This paper traces the origin and development of the step function. A power law with a reference height of 50feet and exponent of 0.1 was originally used to develop the profile; this was projected downward at 50-foot intervals causing discrete steps. This paper proposes a continuous power law formulation of the resulting step function with the commonly used 10m reference height. The exponent is based on a least-squares fit to the original height coefficients. The paper also examines the effect of different exponents on the wind over-turning moment and wind forces for a range of vessel types with different area versus height profiles. These are calculated using both a spreadsheet and available industry software. It was found that a power law of 10m-0.0883 provides the best fit to the final step function and is a continuous function that is recommended for wind tunnel testing for stability purposes.

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